Process and composition for minimizing accumulation of moisture on a cold surface exposed to humid conditions and product obtained thereby

ABSTRACT

The accumulation of moisture on a cold surface exposed to humid conditions which tend to cause condensation on said surface is minimized by applying a coating to the surface which contains unoccluded, water-absorptive particles in admixture with a resinous binder in an amount sufficient to bind the particles together in a adherent coating on the surface, but insufficient to occlude the water absorptivity of the particles. The particles comprise a mixture of cellulosic fibers and water-absorptive, inorganic particles having a bulk density less than 150 kgs/m 3 .

FIELD OF INVENTION AND PRIOR ART

The invention relates to a process and a composition for minimizingaccumlation of moisture on a cold surface exposed to humid conditionswhich tend to cause condensation on the surface and to the productobtained therefrom.

A long-standing problem has been the formation of condensates on theinterior surface of uninsulated roofs and walls usually found inhigh-volume buildings, such as storage spaces, hangers, halls ofdifferent kinds, etc. Many attempts have been made to solve thisdifficult problem manifesting itself in the formation of condensate tosuch an extent that run-off by dripping or coherent flow will result.The problem is multi-faceted, since the solution of the problem byapplication of different forms of insulating material in turn results inphenomena in the form of problems of supporting ability of theconstruction, corrosion between support and insulation, increase inconstruction costs, etc. Moreover, it is desirable on the one hand toapply the insulation in connection with the manufacture of the buildingmaterial in question and on the other hand to apply the insulation onexisting construction in a simple manner without need for disassemblingthe construction.

In an attempt to solve the problem of the formation of condensate,compositions have been prepared including binder and so-calleddiatomite, i.e., the naturally-occurring material kieselguhr, and someadvantageous effects have been obtained, but the problem has not up tonow received a satisfactory solution. Among the disadvantages connectedwith these prior art compositions, it can be mentioned that they requirerelatively high contents of inorganic material that, in view of theformation of cracks, the composition must contain a fiber material, suchas asbestos, and that the drying does not proceed in a satisfactory way,especially at high layer thickness.

It has also been proposed to coat such surfaces with cellulosic fibersand a binder therefor sprayed from separate spray nozzles onto thesurface. This process has not proved practical, however, because it isdifficult to obtain a coating which, when it is weighted down withabsorbed moisture, will adhere to the surfaces treated.

OBJECTS OF THE INVENTION

It is an object of the invention to provide a process and compositionwhich is effective to coat uninsulated cold surfaces for the purpose ofprotecting them against accumulation of moisture thereon due tocondensation.

It is a further object of the invention to provide a process and acomposition which is water-absorptive and which adheres to the surfaceover repeated absorption and evaporation cycles. It is a further objectof the invention to provide a process and composition which iseconomical to prepare and to apply. A further object of the invention isto provide a surface having an absorbent coating, whereby condensate isabsorbed in the coating during cold spells and evaporated therefromduring warm spells.

Further objects of the invention are to avoid the disadvantages of theprior art and to obtain such advantages as will appear as thedescription proceeds.

BRIEF DESCRIPTION OF THE INVENTION

In my copending U.S. application, Ser. No. 800,200, filed May 25, 1977,the disclosure of which is incorporated herein by reference, I havedescribed a process and composition in which the objects of theinvention are accomplished by coating the surface, which is either coldor likely to become cold, with a coating containing water-absorptiveparticles or granules of an expanded, insoluble, inorganic materialhaving a bulk density of at most 150 kgs/m³ in admixture with a binderin proportion such that the water-absorptivity of the granules is notoccluded by the binder. By this process and composition the problem ofcrack formation associated with the prior art has been avoided, so thatit is not necessary to include a fibrous material, for example,asbestos.

It has now been found that the advantages of my prior invention can bepreserved and at the same time greater absorptivity imparted thereto byincluding cellulose fibers in the composition. Thus, thewater-absorptive particles in accordance with the present inventioncomprise a mixture of the cellulose fibers and water-absorptive,heat-expanded, inorganic particles having a bulk density of at most 150kgs/m³.

Quite generally, the composition of the present invention behaves in thesame manner as that of my previous invention. However, the presence ofcellulose fiber in the composition of the present invention givespecific advantages, among which the following are of particularinterest.

(a) By using cellulosic fibers less binder may be used, which, inaddition to the economical advantage thereof, results in lower weightper unit of volume and lower shrinkage when drying after application to,for example, a metal sheet.

(b) The product gives better strength and better binding to thesubstrate since the presence of cellulosic fibers provides for areinforcing effect.

(c) The presence of cellulosic fibers imparts better affinity to waterto the product.

(d) The presence of cellulosic fibers, especially when refined andbleached cellulosic fibers are used, means that a lower percentage ofpigments can be used, resulting in high absorption capacity.

(e) The fact that the product when drying is subject to reducedshrinkage means an increase in absorption capacity and above all animprovement of heat insulation capacity.

While the invention is not to be bound to any particular theory, itseems that the rough surface of the expanded, inorganic material aids inthe binding in the covering layer and improves the moisture absorptionin view of the enlargement of the surface resulting from the roughnessimparted by the granules. Also, the cellulose fibers augment thisroughness and, in addition, act as wicks to lead moisture into and outof the interior of the coating by the capillary action of the fibers.

The process according to the invention can be carried out either inconnection with the preparation of prefabricated material or, can becarried out on existing building construction.

Depending on the material to be protected, for instance, sheet metal,inorganic materials, such as eternite, plastic material or mortar, itmay be advantageous for the binding of the protective material to thesubstrate to apply a so-called primer to the surface before theapplication of the protective material. The protective material in theform of a coating compostion is applied to the surface in question to acertain desired thickness, for instance, 0.5-10 mm, and preferably about1-5 mm. The composition can be applied in any manner, for instance, bybrush coating, roller coating, or spray coating, and the latterprocedure is preferred in connection with application of the compositionon existing construction.

The expanded, inorganic material distributed in the composition in theform of granules can have a varying bulk density, and quite generally,it is preferred that the bulk density is less than about 150 kgs/m³. Apreferred range is 20-150 kgs/m³ and the range 50-90 kgs/m³ isparticularly preferred. Different inorganic materials are conceivable,but a particularly preferred material is so-called heat-expandedperlite. Perlite is a mineral existing in nature and consisting ofliparite or quartz prophyry glass. This natural material of a volcanicorigin contains confined water and, when the material is crushed andheat treated, it expands greatly in view of the evaporization of thewater, and occupies a substantially enlarged volume, which gives itexcellent water absorptivity. It also gives it good insulatingproperties which cooperate with the water absorptivity to minimizecondensation and dripping.

By using an expanded, inorganic material in granule form in conformitywith the present invention, surprisingly good anti-condensationcharacteristics are obtained at relatively low content of granulate. Apreferred range is 5-20 percent by weight based on the compositionbefore application, particularly 8-15 percent by weight and especiallyabout 10 percent by weight.

The granulate is preferably not too fine-grained, since it has beenshown that relatively coarse granules impart particularly goodabsorption characteristics to the coating applied. A grain size of up toa few millimeters thus gives excellent results, and the range up toabout 1.5 mm is particularly preferred. The lower limit, with regard tothe grain size, is not critical, but the fraction of fines should, ofcourse, not be too high in view of the fact that this results inpractical inconveniences in the form of dusting, and the like. Apractical lower limit with regard to grain size, can be said to be about0.01 mm.

Any fibrous form of cellulose can be used, but one of wood origin ispreferred, such as the so-called "hardwood" and "softwood" cellulosicfibers. While originally, these terms denoted source, they have nowbecome associated with the length of the fibers. Thus, hardwood fibersmay have a fiber length of about 3 to 5 millimeters whereas, thesoftwood fibers are somewhat shorter. The shorter fibers are preferredand sometimes it is expedient to run the cellulose fibers through ashear or hammermill with a clearance of about 1.5 mm in order to providefibers in the order of about 1.5 mm length.

Any high-grade cellulose fibers can be used, but it is preferred to usethose which have been chemically refined and bleached to provide awhite, soft, absorbent material. The so-called "Baby Diaper Cellulose"are "R-FLUFT" from Rottuevoss, Sweden, are particularly suitable.

It is sometimes desirable to pretreat the cellulose fibers with a flameretardant, such as a phosphate, for obtaining flame resistance and forthe formation of a carbon skeleton when the coating is excessivelyheated.

The compositions of this invention contain volatile liquid vehiclehaving a resinous binder dissolved or dispersed therein, and expandedgranules distributed therein and, advantageously, a wetting agent bywhich the granules have been pretreated. This wetting agent remains inthe dried coating and results in the improved moisture-absorptiveability of the final insulating coating. The wetting agent is suppliedin relatively small amounts, suitably in an amount of from about 0.1percent to about 2 percent by weight based on the composition.

In addition to said constituents, the composition may contain a pigmentof the desired type, for instance, a white pigment, such as TiO₂, or acolored pigment, such as iron oxide red, iron oxide yellow,chromohydroxide green, phthalocyanine blue, phthalocyanine green, soot,etc., depending on the color desired. To fill up the cavities betweenthe granules, it is suitable to include in the composition also, aso-called extender, which can consist of talcum, calcium carbonate,microdolomite, SiO₂ or kaolin. The amounts of extender and pigment arenot critical and are adjusted in relation to the composition of thematerial. A suitable range of each is about 3 percent to about 15percent by weight based on the weight of the composition before itsapplication. Any conventional binder of the paint art can be used as abinder. The binder may, of course, be selected in accordance with theparticular application, the desired fire-resistancy, etc., but thecharacter of the binder is not critical for providing the desired effectof preventing formation of condensate. Among suitable binders there maybe mentioned homo or copolymerisates dispersible or emulsifiable inwater, for instance, of the type polyvinyl acetate or polyvinylacrylate. Moreover, homo- or copolymerisates dissolved in a solvent maybe mentioned. Furthermore, oxidatively drying binders, for instance,vegetabilic oils, such as linseed oil, alkyds, and etc.

Another type of binder is the curing type of binder, for instance,two-component systems, such as epoxy binders.

The amount of binder can be varied widely in accordance with knowpractices in the art, provided sufficient is used to cause the granulesand the fibers to adhere to each other and to the material coated, butnot so much as to occlude the water absorptivity of the heat-expandedgranules and the cellulose fibers.

When a particularly pronounced fire-resistancy is desirable, inorganicbinders can be used, for instance, of the water glass type. When in thisdisclosure it is said that the composition includes binder and solventit is meant that the composition may contain only binder and solventincluded therein or binder together with further solvent.

The compositions of the invention are coating compositions of thecharacter commonly known in the art as paints and are applied in thesame manner as paints are applied. The compositions contain a volatileliquid which evaporates after the coating is applied and they may bepainted on any suitable surface by brush coating, spray coating, rollercoating, or the like. It is thus applied directly to the surface to beprotected as a liquid coating composition which sets up in situ and canbe applied to the finished structure or to component prefabricated partsthereof.

The invention also covers the finally insulated product, i.e.,substrate, together with insulating coating.

DETAILED DESCRIPTION OF THE INVENTION

The invention may be more fully understood by reference to the followingexample in which the parts and percentages are by weight unlessotherwise specified.

EXAMPLE

A coating composition was prepared by mixing the following ingredients:

    ______________________________________                                        Water                        20.0                                             Hydroxyethyl cellulose 2%-visc. adjust. (thickener)                                                        10.0                                             (Natrosol® HR, Hercules AB, Sweden)                                       NH.sub.4 OH pH adjusted to pH 8 (thickener)                                   Polyphosphate wetting/dispersing agent                                                                     0.1                                              (surface active agent)                                                        Polyglycol ester emulsifier (Arkopal N-090,                                                                0.5                                              Hoechst AG, Germany West) (emulsifying                                        agent)                                                                        Antifoam agent (Antifoam Troy 999, Troy, USA)                                                              0.5                                              (surface active agent)                                                        Ethylene glycol              3.                                               TiO.sub.2 Pigment            5.0                                              Talcum - 20 μm            6.0                                              Vinyl-acrylic copolymer (Mowilith 5152-5,                                     Hoechst AG, Germany West) 50% solids in H.sub.2 O                                                          30.0                                             Cellulose fiber (Baby Diaper Grade)                                                                        2.0                                              ______________________________________                                    

In parallel therewith there is prepared a mixture of water as a solvent(34.0 parts by weight), soya lecithin as a wetting agent (1.0 part byweight) and a granulate of heat-expanded perlite, bulk density 60-70kgs/m³ (10 parts by weight).

The above components prepared separately are mixed to a coatingcomposition, which can be applied by spraying with a spray gun. Thecoating composition was applied underneath to an uninsulated roof ofiron sheet subjected to temperature variations within the range of -10°to +20° C. on the outer side and -6° to +18° C. on the inside at arelative humidity varying between 60 and 95 percent. The composition wasapplied to a thickness of about 1.5 mm, and on the coated surfaces nocondensation can be seen in the form of dropping from the roof, whichnormally constitutes a difficult problem in connection with roofs in anuninsulated state. The effect obtained by using the coating compositionaccording to the invention is in principle based on two effects, namely,the effect due to the insulating and the water-absorbing characteristicsof the layer. If, at extreme conditions, condensation occurs on thecoating, the moisture is distributed in the surface layer withoutdropping occurring, and the moisture evaporates later when conditions ofhigher temperature and/or lower atmospheric humidity exist.

The granules (perlite) used in this example have the followingapproximate chemical composition:

    ______________________________________                                        Silica         SiO.sub.2                                                                             71-75    percent by weight                             Alumina        Al.sub.2 O.sub.3                                                                      12.5-18  percent by weight                             Potassium oxide                                                                              K.sub.2 O                                                                             4-5      percent by weight                             Sodium oxide   Na.sub.2 O                                                                            2.9-4    percent by weight                             Calcium oxide  CaO     0.5-2    percent by weight                             Iron oxide     Fe.sub.2 O.sub.3                                                                      0.5-1.5  percent by weight                             Magnesia       MgO     0.1-0.5  percent by weight                             Total chlorides maximum                                                                              0.2      percent by weight                             ______________________________________                                    

The particle size of the granules lies within the range of 0.01-1.5 mm.Preferred weight ranges and preferred weight fraction for theconstituents of the instant example are given in the table below, alsoshown in percentages by weight unless otherwise indicated:

    ______________________________________                                                               Preferably                                                             Range  about                                                  ______________________________________                                        Vinyl-acrylic copolymer                                                                         15-40    30                                                 Wetting agent     0.05-0.5 0.1                                                Emulsifier        0.05-0.5 0.1                                                Titanium dioxide   3-15    5                                                  Anti-foam agent   0.1-1    0.5                                                Talcum             3-15    6.0                                                Ethylene glycol   1-5      3.0                                                Water             20-40    34                                                 Soya lecithin     0.5-2    1                                                  Granulate (perlite)                                                                              5-15    10                                                 Cellulose fibers  1-5      2                                                  ______________________________________                                    

It can be seen from a comparison of the above example with the parentcase, that there is a significant reduction of contents of copolymer,namely, from 40 percent to 30 percent by weight, which constitutes animportant economic advantage in addition to the fact that the physicalstrength of the dried product is improved. It is believed that this isdue in part to the use of a volatile liquid vehicle for the composition,which evaporates after the composition is applied. It is believed thatthis vehicle saturates the pores of the absorbent particle, i.e., thecellulose fibers and the heat-expanded perlite and helps prevent themfrom being occluded by binders, and the like. Moreover, as the vehicleevaporates from the dry or drying coating, the pores are cleansed of anypossible occlusion.

The pigment TiO₂ used in the above example may be replaced by coloredpigments, as desired, with regard to the color of the coating, such asiron oxide red, iron oxide yellow, chromo hydroxide green phthalocyanineblue, phthalocyanine green, soot, and etc.

By applying the technique of this invention, essential advantages areobtained in connection with insulation of roof or wall constructions ofcurrent interest. Among these advantages, the following may bementioned:

The layer resulting from the coating composition gives an effectiveinsulation and thus a significantly reduced formation of condensate.

Condensates formed in spite of this, are distributed over a largersurface or absorbed in the coating itself, in view of the roughness ofthe surface and the contents of the granules of inorganic material;water absorptivity due to the fibers of the cellulose thus reduce therisk that dropping shall occur.

The composition can be applied in one step to form a relatively thickcoating without any drying problems arising. The composition need notcontain fiber material such as asbestos in order that cracking shall beavoided.

To further illustrate the advantages of the invention, comparative testshave been made, which are presented in the table below:

                  TABLE                                                           ______________________________________                                        Period                                                                        of time         H           A                                                 ______________________________________                                        10      min.        --          --                                            15      min.        --          --                                            30      min.        --          --                                            45      min.        --          --                                            1       hour        --          --                                            2       hours       --          --                                            2       hours       --          --                                            4       hours       --          --                                            5       hours       --          --                                            6       hours       --          --                                            7       hours       --          --                                            8       hours       --          --                                            9       hours       --          x                                             10      hours       --          1.0                                                               after completed                                                               testing, the                                                                  surface is                                                                    completely dry                                            ______________________________________                                    

In the testing on condensation, the apparatus employed was as describedin Ministry of Work's specification D.D.F. B./111 and consisted ofseveral identical copper canisters mounted on an iron framework. Eachcanister was in the form of a cylinder open at the top and closed at thebottom by a right-angled cone. The copper canisters were coatedexternally with the materials under test to give coatings of thethicknesses indicated below. The canisters were attached to the ironframework and then filled with ice and water. Under these conditions,moisture was gradually deposited on the coating by condensation andcommenced to drip from the bottom of the canisters. The drops werecaught in measuring cylinders and the amount of water collected wasnoted periodically. The temperature difference in the tests was 22° C.,i.e., the difference between +25° C. being the environmental temperatureand +3° C. being the temperature of the ice water used. The relativehumidity was 60-65 percent.

In the table, x refers to the time of the first water drop run off,whereas the figures refer to the collected amount of water inmililiters. The column designated H refers to the composition of thepresent application; that designated A refers to the composition ofExample 2 of the parent application.

It can be seen from a comparison the data given in column H and A that,in the comparative tests, run-off in the material without cellulosebegan after nine hours whereas, with that which contained cellulose, thematerial was completely dry after ten hours when the test wasterminated.

It is to be understood that the invention is not to be limited to theexact details of operation or structure shown and described, as obviousmodifications and equivalents will be apparent to one skilled in theart.

I claim:
 1. A process for minimizing accumulation of moisture on a coldsurface exposed to humid conditions which tend to cause condensation onthe surface, which comprises painting said surface with a liquid coatingcomposition having dispersed in a volatile vehicle water-absorptiveparticles in admixture with a resinous binder in an amount sufficient tobind said particles together in an adherent coating on said surface butinsufficient to occlude the water absorptivity of the particles, saidparticles comprising a mixture of cellulose fibers and water-absorptive,heat-expanded perlite having a bulk density less than 150 kgs/m³, thepores of which particles are filled with said volatile vehicle when theliquid coating composition is applied, and allowing or causing thevolatile vehicle to evaporate from the applied coating and from thepores of the particles therein, and in which the heat-expanded perliteis present in an amount of about 5 percent to about 15 percent byweight, the cellulose fibers are present in an amount of about 1 percentto about 5 percent by weight, the binder is present in an amount ofabout 15 percent to about 40 percent by weight and, the volatile vehiclein the amount of about 20 percent to about 45 percent by weight.
 2. Aprocess of claim 1, in which the coating composition containssurface-active materials having wetting-out properties which promoteabsorption of moisture into the dried coating composition.
 3. A processof claim 2, in which the binder is vinyl acrylic copolymer.
 4. A processof claim 2, in which the cellulose fibers are refined, bleached,short-fibered cellulose.
 5. A process of claim 1, in which the coatingis applied to a thickness of about 0.05 mm to about 5 mm.
 6. A processof claim 4, in which the coating is applied to a thickness of about 0.05mm to about 5 mm.
 7. An article of manufacture comprising a surfacewhich, in its unprotected state, tends to accumulate moisture thereonwhen the surface is cold and the ambient atmosphere is humid, whichsurface has a coating adhered thereto which is porous, so that moisturecondensing thereon is absorbed into the coating and in which theporosity is imparted thereto by water-absorptive particles whichcomprises a mixture of cellulose fibers and water-absorptive,heat-expanded perlite having a bulk density less than 150 kgs/m³, whichcoating contains a resinous binder which binds the coating to thesurface and the cellulose fibers and the heat-expanded perlite togetherwithout occlusion of the porosity thereof and having been depositedthereon from a volatile vehicle which initially filled the pores of saidparticles but which is evaporated from the applied coating and from thepores of the particles therein.
 8. An article of manufacture accordingto claim 7, in which said water-absorptive particles compriseapproximately equal portions by volume of the heat-expanded, perlite andthe cellulose fibers.
 9. An article of manufacture according to claim 7,in which the heat-expanded perlite is present in an amount of about 15percent to about 40 percent by weight, the cellulose fibers are presentin an amount of about 1 percent to about 5 percent by weight, the binderis present in an amount of about 15 percent to about 40 percent byweight and, the volatile vehicle in the amount of about 20 percent toabout 45 percent by weight.
 10. An article of manufacture according toclaim 7, in which the coating composition contains surface-activematerials having wetting-out properties which promote absorption ofmoisture into the dried coating composition.
 11. An article ofmanufacture according to claim 9, in which the coating compositioncontains surface-active materials having wetting-out properties whichpromote absorption of moisture into the dried coating composition. 12.An article of manufacture according to claim 11, in which the cellulosefibers are refined, bleached, short-fibered cellulose.
 13. An article ofmanufacture according to claim 11, in which the coating is applied to athickness of about 0.05 mm to about 5 mm.
 14. An article of manufactureaccording to claim 11, in which the binder is vinyl acrylic copolymer.15. An article of manufacture according to claim 7, in which thecellulose fibers are refined, bleached, short-fibered cellulose.
 16. Anarticle of manufacture according to claim 7, in which the coating isapplied to a thickness of about 0.05 mm to about 5 mm.